1. Field of the Invention
This invention relates to catalyst systems for producing phthalate free polypropylene with excellent activity, hydrogen response and high stereo-regularity, and also relates to method for producing a catalyst component and processes for producing polyolefins, particularly polypropylene.
2. Description of the Related Art
Ziegler-Natta catalyst systems for polyolefin polymerization are well known in the art. Commonly, these systems are composed of a solid Ziegler-Natta catalyst component and a co-catalyst component, usually an organoaluminum compound. To increase the activity and stereospecificity of the catalyst system for the polymerization of α-olefins, electron donating compounds have been widely used (1) as an internal electron donor in the solid Ziegler-Natta catalyst component, and/or (2) as an external electron donor to be used in conjunction with the solid Ziegler-Natta catalyst component and the co-catalyst component.
In the utilization of Ziegler-Natta type catalysts for polymerizations involving propylene or other olefins for which isotacticity is a possibility, it may be desirable to utilize an external electron donor, which may or may not be in addition to the use of an internal electron donor. Acceptable external electron donors include organic compounds containing O, Si, N, S, and/or P. Such compounds include organic acids, organic acid esters, organic acid anhydrides, ethers, ketones, alcohols, aldehydes, silanes, amides, amines, amine oxides, thiols, various phosphorus acid esters and amides, etc. Preferred external electron donors are organosilicon compounds containing Si—O—C and/or Si—N—C bonds, having silicon as the central atom. Such compounds are described in U.S. Pat. Nos. 4,472,524; 4,473,660; 4,560,671; 4,581,342; 4,657,882; 5,106,807; 5,407,883; 5,684,173; 6,228,961; 6,362,124; 6,552,136; 6,689,849; 7,009,015; 7,244,794; 7,276,463; 7,619,049; 7,790,819; 8,247,504; 8,648,001; and 8,614,162, which are incorporated by reference herein.
Common internal electron donor compounds, which are incorporated in the solid Ziegler-Natta catalyst component during preparation of such component, are known in the art and include ethers, esters, ketones, amines, alcohols, heterocyclic organic compounds, phenols, phosphines, and silanes. It is well known in the art that polymerization activity, as well as stereoregularity, molecular weight, and molecular weight distribution of the resulting polymer depend on the molecular structure of the internal electron donor employed. Therefore, in order to improve the polymerization process and the properties of the resulting polymer, there has been an effort and desire to develop various internal electron donors. Examples of such internal electron donor compounds and their use as a component of the catalyst system are described in U.S. Pat. Nos. 4,107,414; 4,186,107; 4,226,963; 4,347,160; 4,382,019; 4,435,550; 4,465,782; 4,522,930; 4,530,912; 4,532,313; 4,560,671; 4,657,882; 5,208,302; 5,902,765; 5,948,872; 6,048,818; 6,121,483; 6,281,301; 6,294,497; 6,313,238; 6,395,670, 6,436,864, 6,605,562; 6,716,939; 6,770,586; 6,818,583; 6,825,309; 7,022,640; 7,049,377; 7,202,314; 7,208,435; 7,223,712; 7,351,778; 7,371,802; 7,491,781; 7,544,748; 7,674,741; 7,674,943; 7,888,437; 7,888,438; 7,935,766; 7,964,678; 8,003,558; 8,003,559; 8,088,872; 8,211,819; 8,222,357; 8,227,370; 8,236,908; 8,247,341; 8,263,520; 8,263,692; 8,288,304; 8,288,585; 8,318,626; 8,383,540; 8,536,290 8,569,195; 8,575,283; 8,604,146; 8,633,126; 8,692,927; 8,664,142; 8,680,222; 8,742,040; and 9,068,028, which are incorporated by reference herein.
Most commercial propylene polymerization catalysts currently employ alkyl phthalate esters as an internal electron donor. However, certain environmental issues have been recently raised concerning the continued use of phthalate derivatives in human contact applications. These health concerns from phthalate exposure are driving the art to find a phthalate substitute, or phthalate-free catalyst composition. For example, malonic esters, succinic esters, and diether compounds have been employed as an internal donor for phthalate free catalyst components for propylene polymerization.
Recently, specific forms of diether compounds such as 9,9-bis(methoxymethyl)fluorine and its derivatives have been employed as an internal donor for the phthalate free catalyst component in propylene polymerization, drawing attention for its high activity, hydrogen response and moderate stereo-selectivity. Still, stereo-selectivity of catalyst components employing diether compounds only as an internal donor is not sufficient to reach the stereo-selectivity of catalyst systems containing phthalate or its derivatives, therefore expanding phthalate free polypropylene production via diether compounds has been limited. As such, there is still a need to develop a phthalate free catalyst system providing improved stereo-selectivity for propylene polymerization.